The present invention relates to modular components of a prosthetic joint, and more particularly to modular components of a prosthetic knee joint.
The knee joint basically consists of the bone interface of the distal end of the femur and the proximal end of the tibia. Appearing to cover or at least partially protect this interface is the patella which is a sesamoid bone within the tendon of the long muscle (quadriceps) on the front of the thigh. This tendon inserts into the tibial tuberosity and the posterior surface of the patella is smooth and glides over the femur.
The femur is configured with two knob-like processes (the medial condyle and the lateral condyle) which are substantially smooth and articulate with the medial plateau and the lateral plateau of the tibia, respectively. The plateaus of the tibia are substantially smooth and slightly cupped thereby providing a slight receptacle for receipt of the femoral condyles.
When the knee joint is injured whether as a result of an accident or illness, a prosthetic replacement of the damaged joint may be necessary to relieve pain and to restore normal use to the joint. Typically the entire knee joint is replaced by means of a surgical procedure which involves removal of the ends of the corresponding damaged bones and replacement of these ends with prosthetic implants. This replacement of a native joint with a prosthetic joint is referred to as a primary total-knee arthroplasty.
On occasion, the primary knee prosthesis fails. Failure can result from many causes, including wear, aseptic loosening, osteolysis, ligamentous instability, arthrofirosis and patellofemoral complications. When the failure is debilitating, revision knee surgery may be necessary. In a revision, the primary knee prosthesis is removed and replaced with components of a revision prosthetic knee system.
In revision knee surgery or arthroplasty, bone loss on the proximal tibia can make it difficult to properly stabilize the tibial component of the revision system with respect to the intramedullary canal of the tibia. Various implant configurations are available for immobolization and stabilization of the tibial component, and for distributing the load at the proximal end of the tibia.
For example, it is known to provide integral keels that extend from the stem of the tibial component to the distal surface of the tibial tray. Such a prosthetic implant is illustrated in FIG. 1. As there shown, the tibial component 10 includes a tibial tray 12 and a tibial stem 14 extending outward from and integral with the distal side 16 of the tibial tray 12. In this prior art component, three integral keels 18, 20, 22 extend between the stem 14 and the distal surface 16 of the tray 12. The stem is hollow and can accept a stem extension (not shown) at its distal end 24. The keels 18, 20, 22 serve to help stabilize the implant 10 in the proximal tibia.
It is also known to provide a stepped or terraced sleeve for the tibial stem. Such sleeves are sold commercially as “S-ROM” products by DePuy Orthopaedics, Inc. of Warsaw, Ind. An example of such a system is illustrated in FIGS. 2-5 of the drawings. The tibial component 30 of this prior art system also has a tibial tray 32 and an integral stem 34 that can be connected to stem extensions (not shown) at the distal end 38. However, in this prior art system, there are no keels on the distal side 36 of the tibial tray 32. In this prior art system, a separate, modular sleeve is provided. An example of such a modular sleeve is illustrated in FIGS. 2-4. The modular sleeve is shown at 40 in FIGS. 2-4. The modular sleeve 40 has a tapered interior bore 42 that in which part of the stem 34 of the tibial component 40 of FIG. 5 is received. The tapered interior bore 42 is widest at the proximal end and most narrow at the distal end, corresponding to the shape of the stem 34. As shown in FIGS. 2 and 3, the proximal surface 44 of the modular sleeve 40 has an overall elliptical shape and is generally flat to fit against the distal surface 36 of the tibial tray 32. As shown in FIG. 4, the modular sleeve has a stepped or terraced outer surface 46. The sleeves help stabilize the implant, particularly in case of bone loss, and distribute load.